I've been looking at boxcar doors a lot lately because I'm working on a CNR boxcar that has paired Superior six-panel doors. Here's a prototype photo of the series I'm modelling.
I recently came across a newsgroup posting from Smoky Mountain Model Works that they now offer a Superior/Creco seven-panel door in their S scale detail parts line.
Here's a link to SMMW's S scale parts.
It's nice to see such basic parts being made available, to help us add variety to some of the older kits and RTR out there. I hope SMMW follows up on this with more parts - although in the meantime, I'll be working on my own six-panel doors.